Fanum Martis, present day Famars, a small Roman town unmentioned on the Peutinger map, nor in the Antonine itinerary, seems to have been an important economic actor within the Nervian territory and for its neighboring regions. The first major evidence of a Roman settlement goes back to the Tiberian or Claudian period, although some older vestiges exist. The presence of considerable amounts of raw material (clay deposits, sandstone and iron ore) has enabled its development from the end of the 1^st c. AD onwards, and this to the detriment of Bavay, the territory’s Capital town. The unrest at the end of the 3^rd c. has brought about an extensive campagne of reinforcement of the town walls all over the North of Gaul, amplified during the 4^th c. and is concerning Famars. Its strategic position, controlling the river Scheldt and the Roman roads Bavay-Cambrai and Bavay-Tournai, may explain why Famars received during the 5^th c. a praefectus laetorum Nerviorum Fanomantis Belgicae Secundae, as indicated in the Notitia Dignitatum, pars Occidentalis XLII. The Late Roman castrum, whose building is simultaneous to the city’s rapid demolition, occurred around 320 AD. However, several artefacts indicate a military presence well before. The fortification will be occupied until Carolingian times, when finally the urban centre is transferred to Valenciennes.